The present invention relates generally to an image forming device and more particularly to a printer having a dual-roller overdriven peel mechanism for peeling a protective backing of a label roll from labels attached to the protective backing.
A conventional printer typically has a print head adapted to form images on a printable medium and a platen to press the printable medium tightly against the print head so that the print head may properly form images on the printable medium. Often, the conventional printer also includes a roller to press the printable medium backing against the platen for moving the printable medium through the conventional printer in order to provide a peeling mechanism. Printable media are available commercially in many different forms such as separate sheets of papers, a label roll having labels attached to a protective backing, or simply a paper roll.
The conventional printer requires a pressing mechanism to force or press the platen against the print head and to force or press the conventional peel roller against the platen. The pressing mechanism must be carefully designed to adequately provide a first pressure between the platen and the print head and a second pressure between the platen and the roller. If the first pressure is too low, the print head could not form quality images on the printable medium, while if the second pressure is too low, the roller could not adequately move the printable medium backing through the printer. On the other hand, if either pressure is too high, the printable medium might be trapped therein between and jam the printer. Typically, the first pressure between the platen and the print head is approximately 2 lb/inch, and the second pressure between the platen and the roller is approximately 1 lb/inch.
The peel roller of the conventional printer typically has a surface coated with polytetrafluoroethylene (PTFE) TEFLON(trademark), hereinafter referred to as PTFE. Normally, the PTFE-coated surface of the roller has a glossy smooth surface. Thus, when the roller rotates while pressing against the platen, it will not wear or scratch the surface of the platen and will not make the platen""s surface rough over time. The capability to keep the surface of the platen smooth is highly desirable. Otherwise, a platen having a rough surface will degrade the condition of having even pressure against the print head, and thus will prevent the printer from producing good quality printouts.
The smooth surface of the roller prevents coarsening the surface of the platen, but it also causes some drawbacks to the conventional printer. For instance, due to the smooth surface of the roller, the roller has to exert greater pressure on the platen in order to move the printable medium without causing slips of the printable medium. The smooth surface of the roller also makes it more difficult to maintain accurate traction of the printable medium backing passing through the roller. This would increase possibilities of misalignment of the printable medium within the conventional printer. Moreover, it is easier for the protective backing of the label roll to stick on a smooth surface, as compared to a less smooth surface, of the roller. If the protective backing sticks on the roller, it might jam the printer. The smooth surface is also prone to incur residual adhesives of the protective backing to build up on the rollers surface. As a result, the residual adhesives will likely be transferred to the platen and cause problems in contact with the print head. An improved peel mechanism is therefore needed to overcome the above-mentioned problems commonly suffered by the conventional printer.
An object of the present invention is to provide a printer having a peel roller mechanism that will overcome the above-mentioned problems associated with the roller of the conventional printer. This object is met by providing a dual roller overdriven peel mechanism according to the present invention, as indicated in the claims appended hereto.
The dual roller overdriven peel mechanism of the printer comprises first and second peel rollers rotatably adapted to contact each other to cause the printable medium backing to move through the printer. In a preferred embodiment of the present invention, the first peel roller functions as a driven roller and is coated with tungsten-carbide PTFE materials on its outer surface. The PTFE material allows slip to occur to accommodate a 4% overdrive while maintaining the necessary equilibrium. The first peel roller is coupled to a pair of roller gears respectively positioned at opposite ends of the first peel roller. The surface of the second peel roller is preferably coated with urethane. The printer further comprises a platen for pressing the printable medium against a print head. The platen does not contact the first peel roller, but it is coupled to a pair of platen gears respectively positioned near opposite ends of the platen. One end of the platen is coupled to a motor of the printer through a motor gear mechanism for rotating the platen. The pair of the roller gears and the pair of the platen gears are properly positioned for respectively meshing with each other such that the platen gears will drive both the platen and the first peel roller even though the platen does not contact the first peel roller physically through respective outside diameters.